Field
The present disclosure relates to microfluidic devices and methods of manufacture and inspection of such devices.
Description of Related Art
The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent that it is described in the background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor implicitly admitted as prior art against the present disclosure.
Microfluidic circuits are typically manufactured as planar structures from two substrates which are bonded together and arranged in a carrier. The carrier is sometimes referred to as a caddy. In the case of polymer substrates, thermal bonding and solvent vapour bonding are example bonding methods. In particular, thermal bonding has advantages for biological applications in that no contaminants are involved, for example in comparison to adhesive bonding. Microfluidic circuit elements, such as channels and mixing chambers, are formed at the interface between the substrates by surface structures in one or both of the substrates.
So, in some arrangements, a closed structure can be created by forming a channel, well or similar open formation in one part or substrate, and bonding a second part (such as another substrate, a rigid polymer part or a thin foil) to cover or close the open formation.
Thermal bonding and solvent vapour bonding rely on first softening one or both of the polymer surfaces to be bonded and then pressing the two surfaces together to induce some deformation. In the case of bonding to cover or close an open formation, the bonding of course takes place around the periphery of the open formation.
At this peripheral region around the functional structures, in an ideal case the surfaces at which bonding is to take place are flat, in order to obtain an even bond. Deviations from flatness can be caused by moulding or formation errors (leading to waviness or unevenness of the surfaces) of burrs (raised edges formed around areas which have been moulded or machined). If such deviations are present, they can interfere with the bonding process, and so interfere with the integrity of the finished article, and in particular can affect the integrity of the closed structure—and in some cases, can cause the closed structure to leak.
Due to the shrinkage of the polymer material (when the material cools down after moulding) burrs can be created even if there is a draft angle (that is, even if the formations are chamfered). The height of such burrs depend on, for example, the height of the structures, the draft angle of the structures, the precision of the moulding tool and other aspects of the processing conditions. In general terms, besides causing functional problems arising from the structural deformation, burrs can also cause problems during bonding, for example in thermal bonding or solvent assisted bonding.